Piston pumps are ideal for dry vacuum pumps as they are relatively easy to seal with contacting PTFE seals. The stages in these pumps are typically valved with reed valves or similar non-return valves. This limits the performance of such pumps to a few mbar as lower pressure forces are insufficient to actuate the reeds. Some pumps have used a striker to physically knock the reed valve open. An alternative approach has been to have ports in the cylinder walls that are opened and closed as the cylinder reciprocates. However, none of these approaches is ideal.